Low dielectric constant materials are used as interlayer dielectrics in microelectronic devices, such as semiconductor devices, to reduce the RC delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between metal layers must also decrease to maintain the improvement. Certain low-k materials have been proposed, including various carbon-containing materials such as organic polymers and carbon-doped oxides. Although such materials may serve to lower the dielectric constant, they may offer inferior mechanical properties such as poor strength and low fracture toughness. The eventual limit for a dielectric constant is k=1, which is the value for a vacuum. Methods and structures have been proposed to incorporate void spaces or “air gaps” in attempts to obtain dielectric constants closer to k=1. Some of the suggested solutions incorporate sacrificial materials which are removed subsequent to certain steps within a process integration. Removing sacrificial material generally requires extra steps and expense, and also may require undesirable temperature or solvent exposures associated with the removal of sacrificial material.
Accordingly, there is a need for a microelectronic device structure incorporating air gaps which has low-k dielectric properties and can be fabricated efficiently with minimized disruption of adjacent structures.